Technical Field
The present disclosure relates to monodisperse carboxylate functionalized gold nanoparticles comprising a capping agent layer of pamoic acid and colloidal suspensions thereof Additionally, the present disclosure relates to methods for the size controlled preparation of monodisperse pamoic acid carboxylate functionalized gold nanoparticles and colloidal suspensions thereof using pH and seed mediated growth.
Description Of The Related Art
The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present invention.
Gold nanoparticles (AuNPs) and their chemical preparation have attracted much attention due to their wide application in multidisciplinary research fields such as drug deliver, electroanalysis, sensors, fuel cells, organic photovoltaics, catalysis and glass coloring [Tomar A, Garg G (2013) Global Journal of Pharmacology 7: 34-38.; and Cai W, Gao T, Hong H, Sun J (2008) Nanotechnology, Science and Applications 1: 17-32.; and Saha K, Agasti S S, Kim C, Li X, Rotello V M (2012) Chem. Rev. 112: 2739-2779.; and Aziz M A, Patra S, Yang H (2008) Chem Commun: 4607-4609.; and Matsuoka K, Miyazaki K, Iriyama Y, Kikuchi K, Abe T, Ogumi Z, (2007) J. Phys. Chem. C 111: 3171-3174.; and Cattin L, Tougaard S, Stephant N, Morsli S, Bernède JC (2011) Gold Bull 44:199-205.; and Mikami Y, Dhakshinamoorthy A, Alvaro M, Garcia H (2013) Catal. Sci. Technol. 3: 58-69.; and Sharma V, Park K, Srinivasarao M (2009) Materials Science and Engineering R 65: 1-38.——each incorporated herein by reference in its entirety]. The applicability may come from their properties being highly tunable by size, shape and stabilizing or capping agents [Brülle T, Ju W, Niedermayr P, Denisenko A, Paschos O, Schneider O, Stimming U (2011) Molecules 16: 10059-10077; and HebiéS, Kokoh K. B, Servat K, Napporn T W (2013) Gold Bull 46: 311-318.—each incorporated herein by reference in its entirety].
For the preparation of AuNPs, various methods have been developed. While the chemical reduction of gold precursor with reductant such as ascorbic acid, sodium borohydride and citrate is typical, the selection of the capping agents significantly affects the formation of AuNPs [Frens G (1973) Nature Phys Sci 241:20-22.; and Ji X, Song X, Li J, Bai Y, Yang W, Peng X (2007) J. Am. Chem. Soc. 129: 13939-13948.; and Li C, Li D, Wan G, Xu J, Hou W (2011) Nanoscale Research Letters 6:440.; and Bakshi M S, Sachar S, Kaur G, Bhandari P, Kaur G, Biesinger M C, Possmayer F, Petersen N O (2008) Cryst. Growth Des. 8: 1713-1719.; and Kumar S V, Ganesan S (2011) International Journal of Green Nanotechnology 3: 47-55.; and Londhe P U, More M, Chaure N B (2013) Proceedings of the “International Conference on Advanced Nanomaterials & Emerging Engineering Technologies” (ICANMEET-2013), Chennai, India in association with DRDO, New Delhi, India, 241h_26Ih, July: 317-319.; and Park G, Seo D, Chung I S, Song H (2013) Langmuir 29: 13518-13526.—each incorporated herein by reference in its entirety]. In addition, preparation methods in which a reagent acts simultaneously as a reducing and capping reagent have been proposed because of their simplicity [Dumur F, Guerlin A, Dumas E, Bertin D, Gigmes D, Mayer C R, (2011) Gold Bull 44:119-137.; and Rawat K A, Surati K R, Kailasa S K (2014) Anal. Methods 6: 5972-5980.; and Choi Y, Choi M, Cha S, Kim Y S, Cho S, Park Y (2014) Nanoscale Research Letters 9:103.—each incorporated herein by reference in its entirety]. In any method, the synthesis of gold nanoparticles having narrow size dispersion, i.e. monodispersity, is a crucial aspect of the nanomaterial preparation.
A simple preparation method of AuNPs has been previously reported using pamoic acid (PA) or 4,4′-methylene-bis(3-hydroxy-2-naphthalene) carboxylic acid (FIG. 1) with NaOH at room temperature [Aziz M A, Kim J, Oyama M (2014) Gold Bull 47:127-132—incorporated herein by reference in its entirety]. Although pamoic acid is insoluble in water, it can be dissolved in the presence of NaOH and functions as a capping and reducing reagent to form gold nanoparticles. The thus-formed gold nanoparticles are monodisperse with diameters of 10.8±1.2 nm and carboxylate functionality originating from the pamoic acid. These stable, mondisperse, carboxylate-functionalized gold nanoparticles were prepared without using thiols. Significantly, the size control of pamoic acid capped AuNPs has not been explored in earlier reports.
Pamoic acid is a fluorescent molecule [Baghel G S, Rao C P (2009) Polyhedron 28: 3507-3514—incorporated herein by reference in its entirety], thus the capping with pamoic acid is envisioned to provide gold nanoparticles with significant fluorescent properties as well as the carboxylate-functionality. Fluorescent gold nanoparticles could find utilization in sensors including heavy metal detection, monitoring the growth of a pathogen, imaging, etc. [Guo Y, Wang Z, Shao H, Jiang X (2012) Analyst 137: 301-304.; and Vázquez-González M, Carrillo-Carrion C (2014) Journal of Biomedical Optics 19: 101503-1-12.; and Gyanan, Khatei J (2014) Soft Nanoscience Letters 4: 69-74.; and Jiang C, Xu S, Yang D, Zhang F, Wang W (2007) Luminescence 22: 430-437.; and Chitra K, Annadurai G (2013) Journal of Nanotechnology http://dx.doi.org/10.1155/2013/509628.; and Mérian J, Gravier J, Navarro F, Texier I (2012) Molecules 17: 5564-5591.—each incorporated herein by reference in its entirety]. Some methods have been developed to prepare fluorescent AuNPs. For example, the reduction of gold precursor with NaBH4 in the presence of 11-mercaptoundecanoic acid in toxic organic solvent, reduction of gold precursor with biomolecules, bovine serum albumin (BSA), and etching the pre-synthesized AuNP with hyperbranched and multivalent polymer have been reported [Xie J, Zheng Y, Ying J Y (2009) J. Am. Chem. Soc. 131: 888-889.; and Duan H, Nie S (2007) J. Am. Chem. Soc. 129: 2412-2413.—each incorporated herein by reference in its entirety].
In view of the forgoing, one object of the present disclosure is to provide a range of size controlled and monodisperse pamoic acid capped gold nanoparticles. Another aim of the present disclosure is to provide pamoic acid capped AuNPs having advantageous fluorescent properties. Furthermore, a process for the simple preparation with pamoic acid functioning as both a capping and reducing agent provides an effective versatile approach for preparing gold nanoparticles with a variety of sizes and morphologies, that are monodisperse, stable, and that have advantageous fluorescent properties. Another aim of the present disclosure is to demonstrate preparations for controlling the size of AuNPs in the chemical preparation with pamoic acid through controlling the pH to affect the size. Another aim of the present disclosure is a seed mediated growth method to fine tune the sizes of AuNPs. These methods and treatments provide the ability to tune the gold nanoparticles to desired specifications.